1. Technical Field
The present invention relates to a lighting device, and more particularly, to a lighting device with switchable day/night illumination mode, capable of outputting a visible light at day and outputting a visible light with a specific wavelength at night, respectively.
2. Description of Related Art
Melatonin is secreted by a gland of Pineal body in human brain, and it has the following influences on physiological functions of human: (1) promoting sleep; (2) affecting emotion; (3) sexual maturity and reproduction; and (4) affecting the immune functions.
Moreover, Researches have been found that the production and the secretion of melatonin are mainly influenced by the following three factors: (A) light: light is transmitted to hypothalamus through retinal nerves, and then transmitted to pineal body through the sympathetic nerves, so as to inhibit the secretion of melatonin, therefore the secretion of melatonin can be inhibited in higher level under the darker environment; (B) circadian rhythm: hypothalamus, like a biological clock, can affect the secretion of melatonin, so that the concentration of melatonin secreted by pineal body has a significant variation according to circadian rhythm, and the concentration of melatonin in blood in the night is 6 times higher than that in the day according to researches; and (C) electromagnetic wave: an electromagnetic wave can not only inhibit the ability of pineal body for synthesizing melatonin, but also inhibit the activity of the synthesis of melatonin.
Light is indispensable in daily life. The light perceivable by human eyes is called visible light, wherein the major natural light is sunlight, and the artificial light has various kinds, such as candlelight, incandescent lamps, fluorescent lamps, LED lamp, OLED lamps, etc. Generally speaking, the wavelength range of the visible light is about 450 nm to 750 nm; the color components of the visible light include red, orange, yellow, green, blue, purple, etc.
Besides, researchers also found that melatonin has the highest sensitivity and the second highest sensitivity under the purple light and the blue light, respectively; therefore, generally, the purple light is not directly used as the artificial light for human beings, but the blue light and the red light are often mixed and then be used as the artificial white light. Thus the lighting devices for emitting the white light, such as an incandescent lamp, an LED lamp and an OLED lamp, all of them contain the blue light component. However, it knows that melatonin has high sensitivity to blue the light, thus, if human body is exposed under the blue light for a long period, the phenomenon of melatonin suppression might be induced, and furthermore, insomnia and mood disorders could also be induced. Based on the above reasons, it is able to know that, when during night, it should better for not using any light sources, such that the light can be avoid from being transmitted to hypothalamus through retinal nerves and transmitted to pineal body through the sympathetic nerves, so that, it would not inhibit the secretion of melatonin.
However, for some people having reading habit before bedtime, the artificial light can not be avoided from using to assist people in reading. Although there are sold a variety of night lamps and reading lamps in the market, the light outputted from the night lamps or the reading lamps still includes the short-wavelength light component which will excites people sympathetic. However, researches have been found that, under the condition of one lumen, the orange light having 617 nm wavelength causes the smallest excitation to people sympathetic at night. Accordingly, for the people having reading habit before bedtime, they can adapted the orange light having 617 nm wavelength as the illumination light for reading, so that, they can not only obtain the illumination light for assisting in reading, but also avoid from exciting their sympathetic and causing melatonin suppression.
So that, in view of the sold night lamps and reading lamps are not suitable for using to assist people in reading, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided lighting device with switchable day/night illumination mode.